Compositions for use with electrical connectors



United States Patent 0 COMPOSITIONS FOR USE WITH ELECTRICAL CONNECTORS Harry G. Gossman, Dayton, @2150 No Drawing. Application October 4, 1954 Serial No. 460,233

3 Claims. or. 106-287 The present invention relates to a compound for making low resistance aluminum to aluminum or aluminum to copper or bronze electrical connections of low resistance, low creep, low flow, one which is highly resistant to the efiects of load cycling, temperature, corrosion, oxidization, tension forces, torque forces and vibration and which may be used with either bolted or compression type connectors.

For many years the art of making electrical connections between two like conductors has progressed to the point where bolted connections of copper to copper are satisfactory for the current carrying capacity of the conductor. The connector material has practically the same temperature expansion characteristics as copper and a satisfactory connection is maintained over a wide range of time and temperature. The oxide coating which forms on copper has no serious effect in the resistance of the electrical joint provided the copper is clean when the electrical joint is originally made. If adequate torque is applied to the bolts of the connector, 21 high pull out tension is developed. With an adequate pull out tension developed, the torque resistance to turning of the conductor within the connector is such that the conductor will twist on itself outside the connector before slippage occurs within the connector.

The next advance in the connection art joined copper conductors in a full tension twist splice which was used for many years. This type of connection has now been superseded to a large degree by full tension compression sleeves with multiple indents.

The steps set forth above were followed in the progress of the art in connecting aluminum to aluminum with these exceptions:

(l) The aluminum bolted connector had to be made of a high strength aluminum alloy.

(2) The aluminum conductor had a low flow point under pressure and creep was quite a problem.

(3) Aluminum oxide forms instantly in the presence of air and since it is a good insulator, an aluminum to aluminum connection made in the presence of air has a considerably higher electrical joint resistance than does the equivalent joint made with copper.

(4) Because of the low flow point, the human element of judgment as to the proper torque to apply to a bolted joint became a major element in the resistance value attained in a particular joint.

Steps were therefore taken to control item (3) above by cleaning and scarping the aluminum conductor while it was coated with a petroleum grease or jelly and bolting the conductors together while heavily coated with such grease. This improved the connection resistance considerably but did not materially affect the other deleterious conditions inherent in aluminum electrical connections. The oxidization inhibiting grease actually reduced slightly the pull out tension and the resistance to vibration and torque.

Full tension aluminum compression splices were developed and the inhibiting grease was now loaded with 2,8183% Patented Dec. 31, 1957 ICC a finely divided metallic powder and placed in the compression splice. The conductor was inserted and compressed in multiple space bites. The metallic powder moved the aluminum oxide aside in the absence of oxy gen and an excellent electrical connection resulted. The aluminum was locked in place by the multiple spaced bites so that creep and flow were for all practical purposes prevented and a stable, longlived connection resulted.

The problem of connecting copper to aluminum electrically is much more severe than the connection of one metal to the same metal or its alloy. Two different factors are introduced which multiply the problem of a permanently low resistance connection, namely:

( 1) Unlike coefficients of expansion:

Thermal expansion of copper is .0000177 per degree centigrade.

Thermal expansion of aluminum is .00002545 per degree centigrade.

The alloys of copper or aluminum which are suitable for use as connectors have thermal expansions which vary little from that of their base metal. Thus, because aluminum expands much faster than copper, it will flow or creep at elevated temperatures causing reduced pressures at normal temperatures which, in ttu'n, causes a higher joint resistance.

2) Electrolysis when exposed to weather or moisture: The electromotive position of copper and aluminum with several other materials commonly plated to copper is indicated in the table below where the potential is referred to hydrogen as .000 volt.

Volts Copper +0344 Tin 0.l4 Cadmium O.40 Zinc 0.'762 Aluminum l.33

The metal below will sacrifice itself to the metal above it. Thus the indication from potential diiference is that aluminum will corrode very rapidly in contact with copper when in an electrolyte. The corrosion products of aluminum are insoluble and occupy several times the volume of the original metal. Therefore the corrosion products exert powerful forces at joints between the two metals sufiicient to open the joint further thus exposing a new area for electrolyte penetration and further corrosion. A neutral petroleum grease or jelly with a melting point between 230 F. and 250 F. has been used in the past to seal out the entrance of an electrolyte and prevent electrolytic corrosion. Up to the temperature limits imposed by the grease, corrosion may be controlled. if the temperature limits are exceeded, the grease flows away and the joint is immediately subjected to corrosion at a highly accelerated rate.

Modern tubular connectors are designed with adequate size, length and crimps so that the connection resistance is so low that the connector will operate cooler than the conductor even under short circuit conditions. This, however, is not true for the average bolted or compression type connector used for electrical taps of the nontension type between aluminum and aluminum or copper. The initial resistance of the connector, though expressed in micro-ohms, may double or triple due to the use of aluminum conductors in place of copper. Flow or creep of aluminum can cause the connection resistance to increase many times under extensive load cycling. Short time short circuit conditions on a high resistance connection may cause a burn down failure at the connection.

Under steady load conditions the heat generated in a connector body is dissipated according to the following formula:

'I=current in amperes R=resistance of connection in ohms K=heat radiation constant determined by the dimension and design of the connector T =hot temperature of the connector T =ambient temperature.

Thus it is readily seen that the temperature rise is directly proportional to R and as was previously stated, aluminum connections in the past have initial resistances several times higher than copper and, after several load cyclings, may have a connection resistance many times higher than copper connections using identical connectors. A 40 C. rise above 30 ambient temperature for copper would possibly show a 120 C. rise above 30 ambient temperature for aluminum. Since, in the past, petroleum greases used to inhibit corrosion had melting points between 110 C. and 130 C., we can expect the grease to melt and run away. If new we consider the duty to which a connector is exposed under a short circuit condition twenty times above normal maximum load, applying the proper formula t =a very short interval of time needed to blow a fuse or trip a breaker H=specific heat constant in proper terms for the connector in question the other items are as in the previous formula. Because of the short interval for t the heat dissipated is very small and may be disregarded.

The formula then reduces to:

T can assume a high value because I is now very much higher (400 times for a 20 times short circuit) and if R in addition is high, a burndown may occur or loss of the grease on this short circuit can cause an increase in R with a subsequent failure at normal or short circuit conditions.

The present invention relates to a compound which, when used on aluminum conductors, lowers the resistance of the connection markedly, increases markedly the temperature that the connection will withstand, reduces or eliminates the labor of cleaning the conductor (a new conductor requires no cleaning while an old oxidized conductor is wire brushed without grease), increases the slip torque value of the connection, increases the resistance to electrolytic corrosion, reduces greatly the flow and creep value of aluminum conductor by locking the conductor in place with minute multiple spaced bites or indents and at the same time breaks up and pushes aside the film of aluminum oxide thus exposing the pure aluminum and making individual electrical points of contact while completely surrounded by grease in the absence of oxygen.

In the case of an all copper compression connector, 21 change in formulation makes it possible to increase greatly the pull out tension and torque without affecting the electrical resistance of the connection materially.

4 An example of the compound for making aluminum connections would be a mixture of (by weight) 20 parts of a 10% silica-aerogel thickened grease 25 parts of a 10% tin bronze filter particles, minus mesh, plus 150 mesh 25 parts of 10% tin bronze filter particles, minus mesh, 90% plus 325 mesh For other percent silica-aerogel thickened grease of a different viscosity, the proportions of the metal particles are adjusted to obtain the optimum consistency needed, the smaller particles of metal in greater concentration serving to stiffen the compound or, in lesser concentration, to soften the compound.

An example of the compound for increasing the pull out strength. of copper in'a pressed connection would be (by weight):

20 parts of 10% silica-aerogel thickened grease 50 parts of manganese bronze particles, minus 80 mesh,

90% plus mesh.

The silica-aerogel thickened greases employed in carrying out this invention are preferably thickened lubricants wherein a finely divided non-abrasive silica is used as the gelling agent. Generally, the preparation of these greases into homogeneous mixtures involves the incorporation of a finely divided gelling agent into a liquid lubricant, at ordinary temperatures and with conventional mixing equipment. For example, various methods of preparing silica aerogel thickened greases are described by E. C. Milberger and Lorraine J. Swatik and by Wilbur L. Hayne, Jr. in The Institute Spokesman, January 1953.

While only certain forms of the invention have been described herein, it will be readily apparent to those skilled in the art that many minor modifications may be made herein without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. A composition of matter for use with electrical connectors comprising 70 parts by weight, 20 parts of which consists of a 10% silica-aerogel thickened grease, 25 parts of which consists of tin-bronze filter particles, ten percent being of minus 80 mesh size and ninety percent being of plus 15 0 mesh size, and 25 parts of which consists of tin-bronze filter particles, ten percent being of minus 100 mesh size and ninety percent being of plus 325 mesh size.

2. A composition of matter for use with electrical connectors which comprises 70 parts by weight, 20 parts of which consists of a 10% silica-aerogel thickened grease, and 50 parts by weight consists of tin-bronze filter particles.

3. A composition of matter for use with electrical connectors which comprises 70 parts by weight, 20 parts of which consists of a 10% silica-aerogel thickened grease, and 50 parts by weight consists of bronze alloy filter particles.

References Cited in the file of this patent UNITED STATES PATENTS 2,260,625 Kistler Oct. 28, 1941 2,428,608 Bass Oct. 7, 1947 2,456,313 Pratt Dec. 14, 1948 2,485,176 Waterfall Oct. 18, 1949 2,666,803 Kurlandsky Jan. 19, 1954 FOREIGN PATENTS 206,706 Great Britain Nov. 15, 1923 

1. A COMPOSITION OF MATTER FOR USE WITH ELECTRICAL CONNECTORS COMPRISING 70 PARTS BY WEIGHT, 20 PARTS OF WHICH CONSISTS OF A 10% SILICA-AEROGEL THICKENED GREASE, 25 PARTS OF WHICH CONSISTS OF TIN-BRONZE FILTER PARTICLES, TEN PERCENT BEING OF MINUS 80 MESH SIZE AND NINETY PERCENT BEING OF PLUS 150 MESH SIZE, AND 25 PARTS OF WHICH CONSISTS OT TIN-BRONZE FILTER PARTICLES, TEN PERCENT BEING OF MINUS 100 MESH SIZE AND NINETY PERCENT BEING OF PLUS 325 MESH SIZE. 